This invention relates to a method of solidifying or consolidating a variety of soils such as, for instance, poor quality soils and water-leaking soils by injecting or impregnating a hardener thereinto, and more particularly to a method of injecting a hardener into such soils in which hardener is a water glass solution whose pH value is adjusted to be within the range of from weak (low) acidity to weak (low) alkalinity (pH being from approximately 5 to 9), to prevent the occurrence of almost all types of pollution such as subterranean water pollution and soil pollution.
In this invention, the term "injection or impregnation process" means that a hardener is injected or impregnated into a poor quality soil or a water-leaking soil (hereinafter referred to merely as "a poor quality soil" when applicable) such as those encountered in building foundation excavation work and subway (or underground railway) excavation work, or into the foundation soil of a dam site or of a bank, or into materials to be formed into soils (such as filling earth or discarded materials) thereby to consolidate those soils so that the soils are changed into strongly hardened soils, or cut-offs (water-tightness) are provided in the soils to stop the leakage of water therein.
Recently, constructional pollution such as underground water pollution and soil pollution have frequently occurred because of the use of high-molecular type hardeners. Accordingly, the use of such hardeners has been prohibited. Therefore, there is a strong demand in the art for the development of hardeners which will not cause such constructional pollution as described above.
An injection process employing a water-glass type hardener (hereinafter referred to as "a water-glass type injection process, when applicable) which, hardener is a mixture of a solution of water glass and reacting agent or reactant, is popular in the art because it is considerably high in security. In this conventional water glass type injection process, the gelling characteristic of the water glass in the alkaline range is utilized since the water glass itself is alkaline. In other words, the conventional water glass type injection process utilizes the principle that if an acidic reacting agent is gradually added to a water glass solution with the amount of the acidic reacting agent to be added at a time being gradually increased, the pH value of the resultant mixture solution is lowered while the gelling time thereof is also shortened. At any rate, the gelling of the water glass is effected in the range of pH 11 to pH 10 (Table I). To this end, if such hardener is introduced into irrigation channels or rivers, undesirable influences will be undoubtedly imparted to human bodies, fish, plants and so forth related thereto.
Table - 1 __________________________________________________________________________ Blend (% by weight) Gelation No.3 water time glass Reactant Water min' sec." (%) (%) (%) PH/20.degree. C Temp.20.degree. C __________________________________________________________________________ 42.5 Sodium primary 1.0 Remainder 11.3 20.sbsb.c phosphate Phosphoric acid 2.3 42.5 Sodium primary 1.0 " 11.2 1' phosphate Phosphoric acid 2.5 42.5 Sodium primary 1.0 " 11.1 30" phosphate Phosphoric acid 2.8 37.2 Sodium primary 1.9 " 11.1 1'35" phosphate Phosphoric acid 1.5 42.5 Sodium primary 1.0 " 11.2 31'15" phosphate Phosphoric acid 1.5 __________________________________________________________________________
This difficulty is caused by the fact that in the conventional water glass type injection process the amount of the reacting agent is adjusted so that the hardener is within the alkaline range, thereby to control the gelling time.
Accordingly, in the present invention the idea or principle that "the gelling time of the hardener is controlled by adding the reacting agent to the water glass solution" is put aside. That is, in this invention, based on the idea or principle that "water glass is added to the solution of reacting agent", gelation with the pH value substantially in the neutral range is employed in the injection process in order to eliminate the occurrence of pollution due to the hardener injecting process. Thus, the invention has been obtained.
More specifically, if water glass is added to the solution of acidic reacting agent and the amount of the water glass is gradually increased, the resultant solution will gradually become neutral and the gelation time is shortened. The gelation time is the shortest in the vicinity of the weak alkalinity. If the amount of the water glass is further increased, the pH of the resultant solution becomes alkaline and the gelation time thereof is increased. The inventor has found that such phenomenon could be applied to a hardener injecting process, and has completed a novel hardener injecting method or process in which a hardener prepared to be within the range of from weak acidity to weak alkalinity is employed.